Surface emitting lasers emit laser radiation in a direction perpendicular to the substrate surface. Such lasers have numerous advantages over edge-emitting lasers, including their extremely small size and the relative ease with which a great number of such lasers can be fabricated in a two-dimensional array on a single substrate.
Known surface emitting lasers include a resonant cavity defined by two distributed feedback (DFB) mirrors. The cavity contains a gain medium comprising spacer layers and active, optically emitting layers. Optical pumping of the active layers is achieved by transmitted pump energy through one of the mirrors. Considerable information concerning surface emitting lasers are set forth in the following references: U.S. Pat. Nos. 5,258,990, 4,999,842, and 4,718,070.
Since the pump energy is transmitted into the laser cavity through one of the DFB mirrors, the reflectance of the mirrors is typically reduced at the pump energy wavelength. While this decrease in reflectivity enhances the transmission of the pump energy into the cavity, it also limits the time the pump energy will resonate within the cavity before being transmitted back through one of the DFB mirrors. As a result, the pump energy has a limited opportunity to induce population inversion prior to being transmitted back out of the cavity, thus limiting the efficiency of the laser.